The present invention relates to solid, transparent soaps. Commonly available transparent soap bars contain some sodium soap, some glycerine, perhaps some other polyhydric alcohol such as sugar, a short chain monohydric alcohol and water. The monohydric alcohol is necessary to facilitate dissolution of the sodium soap in the glycerine. Also, the monohydric alcohol contributes to the transparency. A relatively high content of monohydric alcohol and/or water is required in order to effect dissolution of the sodium soap.
For example, to get as much as about 45% sodium soap into the composition, as much as 30% monohydric alcohol is required. Even then, it is not possible to get any more sodium soap into the composition since higher quantities of sodium soap make the bar cloudy and no longer transparent. A generally accepted test for transparency is that one be able to read 14 point type through a 1/4 inch bar of the soap. (See U.S. Pat. No. 3,562,167 patented Feb. 9, 1971.) Another measure of transparency is "translucency voltage" as described in U.S. Pat. No. 2,970,116. It is generally accepted that a soap having a translucency voltage of 30 or less as determined in accordance with the teaching of U.S. Pat. No. 2,970,116 is a transparent soap.
One drawback to the relatively low sodium soap content of prior art bars is that the bar tends to have a relatively short use life. Another problem is created by the monohydric alcohol which is required to dissolve the sodium soap and render the bar transparent. The monohydric alcohol causes shrinkage of the soap in molds on cooling and solidifying. Thus, it is typical for transparent soap to be manufactured by being cast in a large frame, allowed to evaporate several weeks and then cut into bars after the most serious shrinkage has occurred. It is generally not practical to manufacture good quality transparent soap containing monohydric alcohol by casting into individual molds.
Another problem created by the monohydric alcohol is that the soap bars tend to shrink after they are packaged. Packaging in plastic or aluminum wrap is required to reduce evaporation after packaging. Even then, there is a resultant weight loss and one has to actually pack a larger bar into the package than the weight stated on the package in order to compensate for the weight loss which will occur after the packaged bar leaves the factory. The monohydric alcohol is also readily soluble in water and contributes to the short use life of the soap. The scent of the monohydric alcohol also makes it more difficult to perfume the soap in that the alcohol scent interferes with the desired perfume scent. Monohydric alcohols also have relatively low flash points and present a flammability hazard in the manufacturing process.
Another drawback to prior art bars is the difficulty of dissolving additives and still maintain transparency. Such additives might include perfumes, skin moisturizers and etc.
Some prior artisans have avoided the use of sodium soap by using substantial quantities of other types of soaps. U.S. Pat. Nos. 3,793,214, 3,654,167 and 2,580,713 disclose transparent soaps made from liquid soaps. In U.S. Pat. No. 3,793,214, the liquid soap is reacted during the composition step, rather than being previously reacted and introduced as a component. However, the resulting bars lack long use life and really do not provide broad solutions to the above problems.
U.S. Pat. No. 3,562,167 attempts to minimize the quantity of alcohol, water and other volatiles required by employing a nonionic wetting agent comprising a polyalkylene glycol ether of an alkyl phenol in combination with from about 8% to about 22% sodium soap. A nonionic detergent is used in addition to sodium soap. One drawback to such a composition is that these types of nonionic detergents are harsh, drying, and defatting to the skin. Also, the sodium soap content is relatively low.
Yet another technique for avoiding monohydric alcohols, and still get a higher concentration of sodium soap, is to use rather complicated, elaborate mechanical techniques for getting the sodium soap into solution. These may include milling, plodding, refining or the like.
For example, U.S. Pat. No. 3,969,259 to Lages, Mar. 18, 1974, discloses a higher concentration of sodium soap achieved without monohydric alcohol, but teaches that transparency is achieved only with plodding or equivalent working at a relatively low temperature of 100.degree. F. to 110.degree. F. While such mechanical techniques are well known in the art, they are still costly and are desirably avoided.
Another approach to getting more sodium soap into solution is to use a great deal of water or an oil such as castor oil or both. Unfortunately, such bars tend to be too soft and too subject to shrinkage. Also, usually several weeks of aging, six to eight, may be required before the soap actually becomes transparent.
Sometimes a great deal of glycerine, 5-10%, is added as well as water. This too makes for a mushy bar which has a very strong affinity for water. Glycerine can also sting in higher concentrations.